WikiQA is an AS2 dataset [1]} constituted by questions from Bing query logs and candidate answer sentences extracted from Wikipedia, which are then manually labeled. Some questions have no correct answer sentence (all-) or have only correct answer sentences (all+). Table REF  reports the corpus statistics of the versions: raw (as distributed), without all- questions, and without both all- and all+ questions (clean). We follow the most used setting: training with the no all- mode and then answer candidate sentences per question in testing with the clean mode.
<TABLE>